1. Field of the Invention
The present invention relates to an organic light emitting diode including a pixel electrode formed on a substrate, and more particularly, to an organic light emitting diode improved in adhesion with the substrate and reflectance.
2. Discussion of Related Art
An organic light emitting diode is a diode which generates light using an organic material which emits lights when current flows through electrodes, and typically includes a pair of electrodes composed of a pixel electrode and a counter electrode, and an emission layer. The organic light emitting diode optionally further includes, between the pixel and counter electrodes a hole injection layer (HIL), a hole transport layer (HTL), an electron injection layer (EIL), and an electron transport layer (ETL).
Hereinafter, the conventional organic light emitting diode will be described.
The organic light emitting diode includes a substrate, a pixel electrode (hereinafter, referred to as an “anode”) formed on the substrate, an emission layer formed on the anode, and a counter electrode (hereinafter referred to as a “cathode”). The organic light emitting diode optionally further includes a hole injection layer (HIL) and a hole transport layer (HTL) formed on the anode, and an electron transport layer (ETL) and an electron injection layer (EIL) formed on the emission layer. In this case, the anode has a high work function, and is an electrode composed of a single layer formed of transparent and conductive metal oxide such as Indium Tin oxide (ITO) and Indium Zinc Oxide (IZO).
When a voltage is applied between the anode and the cathode in the organic light emitting diode having the above-described structure, holes generated in the anode move to the emission layer through the HIL and the HTL, and electrons generated in the cathode move to the emission layer through the EIL and the ETL. The holes and electrons moved to the emission layer are recombined in the emitting layer to emit the light. The light generated in the emission layer is emitted to the outside through the anode having transparency.
However, the single layer anode has a decreased work function as time progresses, which causes luminous efficiency to be decreased, so that it is not easy to implement colorization or high accuracy which the consumer desires to have. In order to solve the problem of the decreased luminous efficiency caused by the decreased work function, it has been proposed in recent years that silver (Ag) or a silver alloy which has a relatively high reflectance compared to other metals be used to form the anode. The anode using the silver or silver alloy has a relatively high reflectance so that brightness (luminance) of light generated in the emission layer may be further increased.
However, in the process of forming the anode using the silver or silver alloy, an electrically ionized metal may be melted or electro-chemically corroded when the silver or silver alloy is in contact with moisture. In addition, the silver or silver alloy has poor adhesion with a substrate (e.g. a glass substrate), which causes the productivity to be degraded even though it has a relatively high reflectance.